Condition responsive electric switch mechanism



April 6, 1965 c. GRlMsHAw 3,177,321

CONDITION RESPONSIVE ELECTRIC SWITCH MECHANISM Original Filed June 5, 1959 2 Sheets-Sheet 1 v, I A u l 4s nu- A Y as@ Ilmmlul'm--le .af-an E c. GRlMsHAw 3,177,321

CONDITION RESPONSIVE ELECTRIC SWITCH MECHANISM April 6, 1965 2 Sheets-Sheet 2 Original Filed June 5, 1959 3,177,321 CQNDETN RESPNSWE ELECTREC SWITCH MECHANHSM Charles Grimshaw, Fulton, Ill., assigner to General Electric Company, a corporation of New York Original appiieation June 5, 1959, Ser. No. 818,436, now

Patent No. 3,065,323, dated Nov. 20, 1962.` Divided and this appiication Mar. 29, 1962, Ser. No. 183,534

Claims. (Cl. 20d- 140) This is a division of application Serial No. 818,436, tiled June 5, 1959, now Patent No. 3,065,323, and assigned to the same assignee.

This invention relates to electric switch mechanisms and is particularly applicable to automatic temperature control switches for use in connection with electric refrigerators.

Refrigerating machines of the conventional types such as household refrigerators, freezers and air conditioning units, are customarily controlled by means of a switch which automatically starts the machine, in response to a first predetermined condition, such as a predetermined upper temperature, and subsequently stops the machine, in response to a second predetermined condition, such as a predetermined lower temperature. In such switches, a condition responsive element, such as a thermally responsive bellows, provides a mechanical force for controlling the circuit of the machine by opening or closing the contacts of the switch.

A common form of such condition responsive electric switches is generally referred to as a constant dii'- ferential cold control. Switches of this type are ordinarily constructed to initiate the refrigerating operation at a selectively adjustable upper temperature and subsequently to terminate the refrigerating operation at a predetermined number of degrees below the upper temperature. In this type of switch, adjustment of the upper temperature at which refrigeration is initiated, is accompanied by a corresponding change in the lower temperature at which the refrigeration cycle is terminated. The temperature differential, or the difference in the temperature between initiation and termination of the refrigerating cycle, is preset by a separate adjustment, and remains essentially constant for any one setting throughout the entire temperature range of the switch.

Such a switch is expected to provide reliable and consistent sensitivity with continuous use over a long period of years, and the requirements for it are that it be inexpensive, of sturdy construction, and capable of simpliiied adjustment of both the predetermined conditions and condition differential to which it is responsive. In the past, such condition responsive switch mechanisms have been relatively complex, thereby adding appreciably to the over-all cost. This complexity has necessitated the requirement of maintaining close tolerance control over the numerous component parts of the switch, which is essential in order to provide the necessary sensitivity and reliability for the device. The costs of condition responsive switch mechanisms in the prior art, have reflected substantial expenses due to high labor costs and material costs which result from the large number of parts required and the many shop operations required in assembling the switch. In addition, the precision of the component parts which is required for such a switch, usually eventuates in a switch mechanism of relatively large configuration.

It is, therefore, desirable to provide a condition responsive electric switch mechanism which provides close calibration by a simplified adjustment means, and is at the same time simple in construction and easy to assemble, thereby contributing to a substantially lower over-al1 cost. It is further desirable that such a switch United States Patent O 3,3??,32i Patented Apr. 6, 1965 be small in size, thus occupying a minimum space in the refrigerating equipment it is intended to operate. It is additionally desirable that such a switch mechanism be sturdy and have a long life.

Accordingly, it is an important object of this invention to provide an improved condition responsive electric switch which includes a novel adjustment means that enhances the precision of calibration for the switch.

Another object or this invention is to provide an improved condition responsive electric switch which is reliable in operation and includes a simplified adjustment means for Calibrating the switch differential.

It is a further object of this invention to provide an improved condition responsive electric switch that is relatively small in size, sturdily constructed, and has a long life.

In carrying out the present invention, I have provided an improved operating arrangement for a condition responsive switch including a novel adjusting means. In one form of the switch, the contacts are mounted in an insulating base for actuation by a contact operating member. The contact operating member is pivotally mounted on a U-shaped frame which is cooperatively attached to the base, to open and close the switch contacts in response to an external condition responsive means. In this arrangement, a U-shaped toggle spring is provided to produce snap action of the switch contacts. The toggle spring is positioned in continuous compression between the contact operating member and a differential adjusting means. This diderential adjusting means provides linear motion for varying the compression of the toggle spring by knife edge contact with an indented portion of a pivoting end thereof, thus restraining this pivoting end of the toggle spring from any substantial non-linear movement. Fixed stops are also provided to limit the movement of the Contact operating member. Use of this differential adjusting means together with movement of the contact operating member between xed stops, provides an improved control over the toggle spring which precisely calibrates the condition differential ofthe switch.

By further aspects of my invention, additional desirable features may be included in the switch, and the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which I regard as my invention. The invention, however, as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side elevational View of an improved condition responsive electric switch embodying my invention in one form thereof;

FIG. 2 is an end view of the insulating base of the Switch;

FIG. 3 is a side elevational view partially in section and partially broken away, of the switch of FIG. 1, with dotted lines representing certain alternate operating positions of certain movable parts of the switching mechamsm;

FIG. 4 is a sectional view taken along the liue A-A of FIG. 3;

FIG. 5 is an exploded View showing the various parts ot the switch of FIG. 1 with the cover assembly, the base, and the frame, partially broken away;

FIG. 6 is a side elevation view partially in section oi the range .spring and altitude adjustment assembly of the switch; and

FIG. 7 is a slightly magnified side elevational view of the mounting of the outer end of one leg of the ytrame of the switch to the insulating base.

Referring now to FIG. l, there is shown a temperature responsive switch ll which embodies one form of my invention, and often is also referred to as a cold control. The switch I includes an insulating 'oase 2 which, for example, is formed of molded phenolic thermosetting plastic, and a U-shaped frame 3 which is formed from a suitable material such as stainless steel and is securely mounted to base 2 by a means which shall be described in detail hereafter. Frame 3 conveniently also supports bellows assembly d, which provides the desired temperature responsive force, and a cover assembly 5 which includes means for mounting the switch upon a suitable supporting panel.

As best shown in FIGS. 2 to 4, insulating base 2 serve as a mounting for terminals Il and l2, the inner portions of which are contained with la generally U-shaped internal cavity It? of the base. Terminals I1 and i2 are fastened to base 2 at side portions I3 and I4 respectively of cavity It) by means of flanges l5, ld, 17, and IS. These flanges I5, le, 17, and 1S have projecting ends which extend outwardly from terminal side I9 of the base through molded slots 20 and 21 and are staked thereto. Recesses 22 and 23 are provided at the topof portions I3 and le of the cavity lil, to receive upper portions 24 and 2.5 of the terminals, each of which is partially bent inwardly (as viewed in FIG. 2) to thereby furnish additional support for the terminals within the base. Contacts 27 and 28 are housed in the lower or bight portion 26 ofthe cavity lil, and above bight 2d the base includes a centrally disposed upper hollow portion 29, the purpose of which is to provide room for toggle spring 30. This spring, `as will be explained hereinafter, is utilized to provide snap action for the switch contacts.

In order to provide a support for adjusting the spring 3ft, oppositely disposed channels 3l are molded into base 2, and these channels are directed generally perpendicular to terminal side I9 of the base. The channels 3l support a movable pivot member 32 which provides a linearly movable adjustable support for the left side of toggle spring 3f) (as viewed in FIG. 3), the pivot member being movable by differential adjusting screw 33 which er1- gages knurled nut 3d. Screw 33 is accessible from terminal side I9 of the base. Further, details and advantages of the differential adjustment as provided by screw 33, nut 34 and pivot member 32, shall be described hereinafter and the significant value thereof shall then become more apparent. Besides mounting the toggle spring adjusting means and the switch contacts, the base 2 includes a pair of steps 35 and 3d for limiting the movement of contact operating member or lever ltti of the switch. The aciton of the lever liti@ and its cooperation with stops 35 and 3d will be discussed hereinafter.

Contact 2b of switch ll is riveted to terminal lll, and is relatively fixed within the lower portion 26 of base cavity ld. Bounce damper 37 is also fastened to terminal Il at the reverse side thereof from contact 28 and by the same rivet, to provide a slight cushioned movement of contact 2? when the contacts -are closed. Contact Z7 is the movable contact of the switch and it is riveted to movable leaf spring strip 3S. Strip 38 is riveted to terminal l2 at point 39, and a weld is also provided to guarantee electrical conductivity between strip 33 and terminal l2.

By riveting bouce damper 37 on the reverse side of terminal Il from relatively fixed contact 28, a spring type of cushioning is provided between contact 2S and lower side itl or rib 4l of the base. The bounce damper 37 comprises a leaf spring having a waved end section which engages, but is not fixed to, the rib side dit. The spring flexes to provide a cushioning action, and also `a limited sliding movement of the waved end occurs .along rib side 4t) to aid in the cushioning action, as the contacts are closed. It has been found that use of this bounce damper materially extends the life of the switch since the contacts are substantially precluded from bouncing open i after they have once closed. rthis results in minimal welding of the contacts and a reduction in contact erosion, which often in the past have presented the problem of restricting the life span of the switch contacts.

At the lower portion of terminal I2 (as viewed in FIG. 2 of the drawing), there is provided an outwardly extending ridge portion ft2, the purpose of which is to properly position portion 38a of the contact carrying strip 3S, to produce the proper contact pressure or biasing fonce between contacts 27 and 23.

Insulating base 2 of the switch l, as thus has been clearly shown, provides a secure mounting for the contacts 27 and 2.8 of the switch as well as associated terminals lll and l2. In addition, base 2 provides convenient external access to and a mounting for the differential adjusting means which varies the snap acting biasing force of ltoggle spring 3d. Furthermore, base 2 also includes fixed stops for limiting the travel of the operating member of the switch.

In addition to the aforementioned features, the base construction has another significant advantage, which will now be discussed. This feature is the manner whereby frame 3 is mounted upon insulating base 2.

insulating base 2 contains a pair of integral molded ears d5 which project outwardly rfrom the opposite sides 44 and L5 thereof, asbest shown in FIGS. 2 and 4. These ears serve as an important part of the mounting means for frame 3, las hereinafter will become apparent. The detailed configuration of these ears is best shown in FIG. 7. As viewed in FIG. 7, each ear includes upper and lower parallel sides 46 and 47 respectively and forward and rear sides t8 `and i9 respectively. A lower angular side Sil connects side dit with side 47. The rear side 49 of each ear is coplanar with and actually forms an outward extension of lthe associated rear edge 5l or 52 of base 2. The ears d3 and rear edges 5l and 52 of insulating base 2, all serve as a secure supporting means for mounting the switch frame thereupon; but to more completely describe the interengagement between my switch frame and supporting base, a detailed description of the improved construction of the frame is first desirable.

Frame 3 is very important to the housing structure of the switch and, as previously intimated, it offers a multiplicity of advantages. It is generally of U-shaped configuration and is prefer-ably formed by bending a single flat piece of sheet metal into oppositely -disposed legs 7d and connecting portion 7l. The configuration of frame 3 is best illustrated by the exploded View of FIG. 5. Legs 7d extend generally perpendicular to connecting portion 7l and at their outer ends 73 each leg includes tan inwardly bent tab 74, the flange of which is inclined slightly upwardly (as viewed in the drawings) towards connecting portion 7l. (See FIGS. 3, 5, land 7.) Adjacent to tabs 7d, in each leg 7d there is provided slot 76, which is best shown in FIG. 7. Each slot 7 6 has generally parallel upper and lower edges 77 and 78 respectively land generally parallel outward and inward edges 7 9 and 30 respectively which are generally perpendicular to the upper and lower edges. The upper portion of inward edge dit is stepped inwardly to provide a small step Sl. Between each outward edge 79 of slot 76 and lower edge 78 there is an angular edge 82, a portion 83 of which is convexly curved inwardly and faces diagonally, in the genenal direction of step di. Extending downwardly and inwardly from the lower edge 34 of each leg '70 of the fname there is tab 85. Outward side edge de of each tab 85 is generally aligned with stepped edge 8l on the upper side of each slot 76, as best shown in FIG. 7.

To securely mount switch frame 3 upon insulating base 2, cover plate 5a, included in the cover assembly 5, may be conveniently used as a lever. For this purpose, cover plate 5a includes a pair of spaced tongues 7 which are disposed near forward end 88 of the plate and form corner portions thereof. The plate 5a further includes side aire/,sei

S9 which extend downwardly from the fiat surface 9@ of the plate between forward end S5 and rear end 1n assembling frame 3 upon base 2, legs 7@ ofthe frame are tinst pulled slightly apart so that ears d3 of the base may be received within frame slots 75. At this point in the assembly operation, frame 3 rests loosely upon the base 2, with the weight of the frame urginfy edges 86 of frame tabs against rear edges 51 and 52 of the base, and ears d3 fitting loosely within receiving slots 76. rthe operating mechanism of the switch is then mounted within the frame, tl e details of this mechanism to be later described. The cover assembly 5 is thereafter mounted upon the frame. Tongues d'7 of cover plate Sa are slipped underneath the inwardly bent tabs 7d of frame legs 7b, the inclined configuration of the ftab 74 facil'tating this step. The rear end Q1 of the plate or the vicinity thereof is thereupon pressed downwardly. Side flanges S9 then overlap upper edges 92 of frame 3 to securely retain legs 7d from any outward movement. Rear end d1 of the cover is fastened to connecting portion 71 of the frame by spring clips 93 which shall be described hereinafter.

Tongues S7 of cover plate 5a serve as levers to pry certain edge portions of slots 7o and tabs 35 on each frame leg into firm engagement with base 2. Essentially, this iirm engagement amounts to a three-point suspension of each frame leg 7d upon base 2. A first point for this suspension is provided by the engagement of step S1 of slot 76 with an upper part of rear side t9 of ear d3; inwardly convex edge d3 of slot 76 engages a point on lower angular side 5@ of ear d3 to furnish a second point of contact; and side edge 86 of the inwardly extending tab S5 of each frame leg, engages rear base edge 51 or S2 to provide a third point of suspension.

A pair of dimpies 9d are formed on the lower side of cover plate 5a, to provide points of mounting Contact for supporting the cover upon raised portions of base 2. These raised portions 95 project upwardly (as viewed in FIG. 5) from upper surface 96 of the base on opposite sides of central hollow portion 29. The upper surfaces 97 of the tongues 87 of the cover plate contact lower forward edges 9d of tabs 74 forwardly of the raised portions 953', and the rear end 91 of the cover plate is pressed downwardly upon the frame, the tongues d'7 thereby thrust the tabs upwardly from surface 95 the proper distance. Tabs 7d of the frame and tongues 87 of the cover, bend slightly in assembly to facilitate a minimum tolenance buiid-up, by removing the manufacturing tolerances.

The features of the switch frame and base thus provide a very secure mounting for the frame upon the switch base, which mounting is achieved by a simplified assembly procedure.

Turning now to the operational aspects of my im proved switch, to actuate the switch contacts, 1 have provided contact operating member 1d@ which includes contact `actuating arm 1611 riveted thereto at the near side of ymember 161i as shown in FiG. 5. This operating member is actuated by a temperature responsive bellows 121, in opposition to a range or control spring 12d, to operate the switch contacts. To pivotally support contact operating member 1d@ in frame 3, trapezoidally coniigured siots 1132 are formed in legs 'ii 7d and connecting portion 71. -eivoted within slots 162 of the frame are projecting shoulders or trunnions 103 of member 1nd, which are spaced forward of hanged end 16d as shown in the exploded view of FG. 5, end 1de being hanged to stiften the member 10b. Each of trunnions 1% has a knife edge 1de" which is formed by a rear side sloping downwardly towards end 1M. When the shoul- 'ers 1&3 of operating member 1d@ are mounted in slots 1h22, knife edges 1% pivot at sharp corners 1de of each slot, thereby providing a precise support for pivotal motion of the operating member. To provide clearance for the outer ends 1% of trunnions 1153, each of slots 192 of the frame is disposed in a slightly indented section 1d? thereof. When operating member 16) is` pivotally between slots mounted in the frame, outermost end 19S of each trunnion 163 has clearance for movement within shallow recess 197er which indented section 107 provides.

Spaced slightly forward from shoulders 103 of operating member Mtl are a pair of raised knife edges 165i, the purpose of which is to provide accurate pivots for supporting bearing 11d thereon. Bearing 11d, as will be later explained, furnishes a means for transmitting bellows force to operating member 1th?. Knife edges 1919 are configured cross-sectionaily in the shape of an inverted V, and project inwardly towards the center of opening 111 of the operating member to receive grooves 112 of the bearing. Grooves 112 are also in the configuration of an inverted V so that when bearing 11d pivotally rests upon operating member 1%, distinct pivot locations are provided by knife edges 199 of the operating member and the lines of mating contact of grooves 112 adjacent the apexes of grooves 112.

The particular construction of bearing 11? and its arrangement for transmitting force to the operating arm comprises the invention of Richard W. Cobean, and this construction and arrangement are described and claimed in his copending application Serial Number 818,437 filed .tune 5, 1959, now Patent No. 3,065,320, and assigned to the same assignee as the present invention. As shown, the bearing includes upper shoulders 113 within which aforementioned grooves 112 are formed, depending parallel pairs of struts 114, and base 115. To provide a force transmitting seat for altitude adjusting screw 11d, cup-shaped recess 117 is formed in base 115, and it has a slightly iiattened annular seat 118 upon which shoulder portion 119 of screw 116 rests. The primary function of bearing 116 is to transmit the difference force between range spring 12d and bellows 121 to the operating member 1nd, and the operation thereof shall become more readily apparent hereinafter as my description progresses.

To insure that the inner portions of pivoting knife edges 165 of the operating member have ample room to pivot within their mating slots 102 of frame 3, and minimize frictional contact between side edges 123 and 124i and the frame, the outer ends 1h25 of trunnions 1193 are made oblique to the length thereof. Operating member 1d@ is thus widest approximately at the ends 105er of knife edges 1ti5 so that ends 105e locate the operating member between sides 171 of the bellows cup 170. (See B1G. 4). To locate the operating member between frame legs 7i! before mounting the bellows assembly thereto, curved protuberances 122e and 122!) are formed on the edges 123 and 124i of the operating member. Spaced forwardly from protuberance 12ga, and adjacent edge 123 of the operating member, manual stop extension 125 projects upwardly in a direction generally perpendicular to the face of the operating member. Upwardly directed point 126 is provided on this extension to contact a manually adjustable control means for opening the switch contacts.

To provide a means for continually biasing operating member 1d@ in the direction of the closed position of the switch contacts, or with a continuous clockwise moment of biasing force about knife edges 165, as shown in FiG. 3, I have provided the previously mentioned U-shaped toggle spring 3b. As best shown in FIGS. 3 and 5, toggle spring 3d has indented end portions 127 and 12d for mounting the spring in continuous compression between pivot member 32 and operating member 10d, respectively. Knife edge 129 is formed in the forward end of member 1th? to engage indented portion 128 of the toggle spring, and thereby receive the transmission of continuous biasing force of the toggle spring.

To support the indented or pivoting edge 127 of toggle spring 3d, pivot member 32 has a central knife edge 13d which inclines slightly downwardly (as viewed in FiG. 5) to engage indented portion 127 of the spring,

f forming a knife edge contact therewith. At each end' of pivot member 32 a pair of spaced doubly bent hngers 131 extend outwardly. These fingers 131 specifically are formed at the corners of the member 32, and together with body surface 132, they provide bearing surfaces for sliding movement of member 32. 1n particular, the ngers fit within channels 31 of the base, which serve as guides for the sliding movement. On the side opposite to downwardly inclined knife edge 131i, pivot member 32 has an upwardly extending central flange 133 engaged by the leading or forward end 134 of differential adjusting screw 33. Externally accessible screw 33 engages knurled nut 341 which has been pressed into base 2, and by manual rotation of the screw, it may be moved toward or away from the toggle spring 311. By means of the leading end 134 of the screw engaging flange 133 of the pivot member 3 2, the compression of the toggle spring 311 may be adjusted by the knife edge contact between edge 130 of the pivot member and indented pivoting edge 127 of the toggle spring. Channels 31 serve to guide the movement of the sliding pivot member so that pivoting edge 127 of the toggle spring is moved horizontally (as viewed in FIG. 3) with a linear motion. Axial movement of screw 33 thus varies the biasing force supplied by the toggle spring and thereby varies the temperature differential of the control switch, while pivot member 32 within channels 31 precludes any signicant vertical movement of the pivoting edge 127 of the toggle spring. Different thicknesses of toggle springs may be utilized in various switches, to provide the range of temperature differentials which is required.

As previously noted, base Z has molded therein fixed stops 35 and 3o which are provided for limiting the upward and downward movement of operating member 11i@ between two fixed points. By limiting the movement of the operating member between these stops, the possibility of reaching the limits of the particular toggle spring is thereby precluded, the biasing force provided by the toggle spring being within the most desirable range of the spring potential.

The combination of my limiting stops 35 and 36 coupled with the dilferential adjustment of toggle spring 33 by linearly guided movement of pivot member 32 with its variably positioned knife edge point of contact, provides a substantially improved tolerance control over the offset of the spring. In designing toggle springs for use in switches such as those incorporating my invention, the quality known as offset is an important characteristic which it is most desirable to control. Oifset may be explained in my switch as the distance which a line between the indented pivoting edge 127 of the toggle spring 33 and the operating member pivots 105 is displaced from the point of engagement of the operating member with the movable indented edge 123 of the toggle spring. The stops 35 and 36 together with the positive linear adjustment of the pivoting edge 127 of the toggle spring, provide a very close control of the offset of the toggle spring of my switch in both positions of the spring. By this improved control, l thereby achieve lower offset distances for the toggle spring, resulting in higher switch energy for a given set of parts.

To provide a continuous downward biasing force upon bearing 1111, and therefore a continuous counterclockwise moment of biasing force upon operating member 11111 about pivoting knife edges 135, l have utilized the previously referred to range spring 12d, Range spring 1211 transmits its compressive force to altitude screw 11o via nut 135 which is threaded on screw 116. To provide relatively precise seating contact, upper end 121m and lower end 12311 of spring 1241 are ground square. Lower end 12tlb of the spring rests upon upper annular flange surface 13511 of altitude nut 135, and upper end 12AM of the spring bears upon lower annular surface 136 of cam follower eyelet 137.

By varying the :compression of range spring 1211, the temperature level at which my cold control operates may be adjusted. To effect this variation, l provide manually adjustable cam 133 which -is rotatably mounted on cover plate 5a by shaft 142, and engages pivotally mounted cam follower 139. Follower 139 is responsive to the rotary position of cam 138, and cam follower eyelet 137 is pivotally mounted thereon. Cam 133 may be constructed of die cast zinc and includes gradual sloping portion 1411, and abrupt sloping portion Mila, as best shown in FlG. 3. These sloping portions 1d@ and llt-illu of cam 133 serve to provide a manual adjustment for the c-ompression of range spring 1211 by rotary engagement with curved extension 141 of cam follower 139. To facilitate the manual rotation of cam 138, shaft 142 is secured thereto by some suitable means such as a press lit. Most of the cam is disposed within circular recess 1413 which is formed within raised annulus 144 of cover plate 5a, as shown best by FIG. 3. An annular shoulder portion 145 of cam 133 extends upwardly through an aperture 1416 in the cover plate and key projection 147 of the cam enters a mating slot of a knob mounting adapter 143 which is aixed to knurled neck 111241 of shaft 1412. Spring washer 141341 is positioned between adapter 14S and the upper surface a-rea -of the plate immediately surrounding aperture 146. To provide a limiting stop for the rotation of cam 133, downwardly lanced portion 144:1 projects slightly into -recess 143, to engage lateral extension 149* of cam 133. Extension 149 also serves to contact rearward facing surface 126e of point 12o on extension 125 of operating member 1311, to provide a manual-off pivoting movement of operating member 11111 and thus open the switch contacts,

Cam follower 139 of the switch 1 is pivotally mounted in connecting portion 71 of f-rarne 3 by means of fingers 151D which are bent perpend-icularly upward (as viewed in FG. 5) and engage the upper edges 151a 1of spaced slots 151 of connecting portion '71. Sharp inner edges 152 are formed at the base of lingers 151i. To provide a slight upward biasing of inner edges 152 of fingers 153 against upper edges `151e about which the cam follower pivots, spring tab 153 is provided in frame connecting portion '71. Tab 153 is bent slightly inwardly and then outwardly from connecting lportion .71 and furnishes a spring biasing force against cam follower 139 by engaging central nose 15dk thereof. The nose 154 specifically engages and is biased by inwardly extending angular shoulder portion 153a of the tab 153.

Cam follower 139 also includes a pair of spaced ridges 155 on its underside which extend downwardly, as best shown in FIG. 3, to pivotally support cam follower eyelet 137 thereon. Upwardly extending tabs 156 of eyelet 137 are received by spaced slots 157 at the outer ends of ridges 155, and then turned outwardly to pivotal-ly mount the eyelet on the ridges 155 of the undersurface of the cam follower. (See FIG. 4.)

To provide access to range screw 116, apertures 153 and 159 are provided in the cam follower 133 and cover plate 5a respectively and these apertures are in alignment with the altitude screw 116 so that a presetting adjustment may be made of the 4range spring compression by adjusting the relationship of altitude screw 116 with its associated nut 135, after the control switch is assembled.

For mounting switch 1 to a suitable supporting panel, mounting extensions 1o@ are provided at each end of cover plate 5a. Each extension includes a threaded aperture 161 t-o engage a suitable mounting screw.

Turning now to the bellows assembly 1 of switch 1, which I have chosen as a typical condition responsive means, I have provided bellows cup or housing 171i for supporting and containing bellows 121. Bellows cup 17@ includes upwardly extending flanged sides 171 for straddling the lower portion of frame legs 70. Sides 171 cover the lower portion of shallow recesses 107e (as viewed in FlG. 4) to protect the outer ends 1113 of trunnions 1113 of the operating member. To securely mount bellows cup upon frame 3, a pair of spaced toes 172 extend outwardly from inner end 173 of the cup to engage tabs 85 of the frame by conveniently slipping underneath. Tabs 85 of the frame thus serve the twofold purpose of both engaging the base to help mount the frame thereon, and receiving toes 172 of the bellows cup 17@ to help mount the bellows assembly thereon. For locking the bellows assembly rigidly against lower edge Se of each frame leg, a pair .of spaced slots 174 are provided, each of which is adjacent to outer end 175 and sides 171. Adjacent to rear end g1 of cover plate 5a, a pair of spaced laterally extending indentations 91a are formed in the upper surface thereof. For rigidly clamping rear end 91 of cover fplate 5a and louter end 175 of bellows cup 171i against upper edge 1176 and lower edge v177 respectively of frame connecting portion 71, I utilize two spring clips 93 eaoh of which compresses the adjacent ends of cover plate 5a and bellows cup 171i against the edges of connecting portion 71, by engaging an indentation 11a of the cover and an oppositely disposed slot `17d `of the bellows cup. This is -best shown in FIG. 3. Upper rear tongues 92a may also be formed on legs 7l) `of the frame near connecting portion 71 to serve as positioning guides for the cover. These tongues may also be bent over to additionally secure the end of the cover plate .to the frame, 'but this is not at all necessary. The spring clips 93 are thereby utilized to both rigidly secure and lock the cover assembly and the bellows assembly against the frame.

For insuring the alignment of outer end 175 of the bellows cup with lower edge 177 of frame connecting portion 71, spacml tabs 178 project downwardly from the lower edge 177, and their inner faces 178a enter squared recesses 179 which are adjacent to the outer end 175 of the bellows cup.

Bellows cup 170 also includes a depending flange 180 with projecting arm 181 extending therefrom `for supporting capillary 182. Capillary ,182 is connected to a suitable bulb 183 and contains a thermally responsive fluid such as methyl chloride or dichlorodiiluoromethane.

For furnishing the temperature responsive actuating force for the switch, bellows 121 is mounted with the bellows cup 170. A restraining annulus 13d having supporting arms fitted into an annular `groove in the inner wall of the bellows cup, restricts the upward movement of bellows 121. To provide the transmisison area for the temperature responsive force, bellows 121 has a central cupshaped recess 1Z1a within which a smaller recess 121i) is also contained. Recess 1211!: has an upwardly projecting nose centrally disposed therein, which bears against lower tip 116e of altitude screw 116. Altitude screw 116 also receives the -downward biasing force of range spring 12) and transmits the difference of the forces of spring 121i and bellows 121 to bearing 110 and the operating member 1%. More specifically, as mentioned above, shoulder 119 of altitude screw 116 transmits the difference force to bearing 112 by engagement with flattened annular seat 113 thereof.

Frame 3 of switch 1 also includes drainage holes 1155 in each leg 711, the purpose of which is to provide for the drainage of any condensation which collects within the switch.

Considering now the operation of the improved condition responsive switch :mechanism which I have disclosed, let us lirst assume that this switch is utilized with a refrigeration machine, to control the compressor unit thereof by means of opening and lclosing its electrical contacts in response to bulb or capillary temperature. Assuming that the bulb 183 or capillary 182 is at a temperature slightly above the on temperature of the cold control, the contact operating member 111? would then be in the position 101m, as shown by the dotted lines of FIG. 3, with the contacts biased to their normally closed position. At this position, the load on operating member 100 at knife edge pivot points 109 is low, being only enough .to maintain engagement of the bearing with the operating member and altitude screw at knife edges 109 lil and shoulder 119 respectively. At this time, the bellows force is nearly equal to the range spring force, and the toggle spring 30 is holding the operating arm against stop 35. Toggle spring Sil, which is shown by dotted line 30a, is then in a position off of dead center its maximum distance. It, therefore, supplies its maximum biasing force against knife edge 129 of operating member 191i. Bearing 110 can swivel about shoulder 119 of altitude screw 116 as necessary, to maintain a unique engagement at knife edges 1119 and shoulder 119, and to transmit the difference of the range spring force and the bellows force to the operating member as a force moment about pivo-ting knife edges of the operating member. This force moment, as above indicated, is relatively low.

With the compressor of the refrigerating machine then in operation due to the contacts of the switch being closed, substantial cooling in the vicinity of the bulb or capillary tube of the bellows assembly ensues. As the compressor pulls down the temperature, the capillary or bulb senses this dropping temperature and consequently causes the temperature responsive fluid contained therein to decrease the internal vapor pressure on the bellows. The force exerted upwardly upon range screw 116 by the bellows thus gradually decreases, and the temperature drop causes an increasing resultant downward force to be exerted upon pivot points 199 by range spring 129. In other words, bearing 116 exerts a force moment upon operating member 100 at knife edges 109 of member 100 which is determined by the difference between the forces of the range spring and the bellows. Toggle spring 3@ exerts a continuous biasing force upon knife edge 12? of operating member 10i), and this force has a clockwise moment about pivot points 1% of the contact operating member (as viewed in FIG. 3). When the temperature reaches a point where the counterclockwise moment of the force transmitted to pivots 109 by bearing 110 just exceeds the clockwise moment of the toggle spring biasing force at knife edge 129 of operating member 1st), the operating member 101i snaps to the solid or lower position as shown in FIG. 3. The contacts are thus opened, by the downward movement of pin 10111 of actuating arm 1411 against an extension 38b of leaf spring strip 3S which carries movable contact 27. With the contacts open, the circuit to the compressor motor is opened, to interrupt the cooling operation.

With the contacts open, toggle spring 30 is a minimum distance olf of its dead center position, and it produces a slight but definite clockwise biasing force upon the operating member. As the temperature of the capillary or bulb then starts to increase, the vaporization of some of the fluid therein causes the bellows internal pressure to increase accordingly. At first the bellows will not move because the force of the range spring is sufliciently greater than the opposing force of the bellows. But with further temperature increase in the vicinity of the capillary or bulb, the bellows internal pressure increases until the bellows force becomes more nearly equal to the range spring force, and the counterclockwise moment of the diiference force is exceeded by the small clockwise moment of the toggle spring biasing force. At this point, the spring Sil toggles the contact operating member to its upper position. This, of course, allows the contacts to move to the on position and again energizes the circuit to the compressor.

To adjust the differential temperature of the control switch, that is, to adjust the difference between the on and oli temperatures of the control, one needs merely to rotate the differential adjusting screw 33 which is externally accessible from the terminal side of insulating base 2.

For varying the temperature levels at which the switch is responsive to open and close its contacts, shaft 142 is rotated. This changes the position of cam 138 and thereby varies the compression on range spring 121B. Turning the shaft 142 in a counterclockwise direction causes the cam slopes Mtl and lili-ila to move over raised surface Ml of the cam follower and therby variably deflect the cam follower 139 and pivoted eyelet 137, to gradually increase the compression upon range spring 120. Increasing the range spring compression means that added bellows pressure is required for operating member lltltl to toggle to the on position, and therefore increases the temperature level at which the contacts of the cold control will respond. The rotation of the shaft 142 in other words raises or lowers the on? and off temperature together, while not materially affecting the differential therebetween. Y

For conveniently presetting the force of range spring 120, a factory or shop adjustment of altitude screw 116 may be made.

In assembling the cold control switch embodying the present invention, I preferably utilize several subassembly operations, followed by the main assembly procedure.

A base sub-assembly is achieved by mounting the fixed and movable contacts 28 and 27, supporting spring strip 38, and the associated terminals lll and l2 on insulating base 2. Knurled nut 34 is pressed into its position in the base, and differential adjusting screw 3? is threaded into engagement therewith.

A cover sub-assembly is put together by first inserting lubricated cam 138 in aperture ldd of cover plate 5a. Spring washer lesa and knob adapter 1F98 are then placed on the outer side of the cover around projecting portion M5 of cam 138 and shaft M2 is press fitted into the cam to retain cam 138, washer 1480i and adapter M8 on the cover. The inserted portion of shaft 142 is knurled (not shown) to provide torsional resistance and the lower lip of the shaft is slightly staked to preclude the possibility of its being pulled loose.

Sub-assemblies are also provided for the range spring 124D, altitude adjusting screw M6 and associated nut l35; lcontact operating member l@ with actuating arm tell riveted thereto; and the cam follower 139 with eyelet 1137 stakes thereto.

lBellows assembly d has also been constructed prior to my main assembly operation.

rThe main assembly operation for this cold control switch then is commenced by the sliding of pivot member 32 into channels 3l of the base 2 so that flange :i3-3 thereof engages the forward end ldd of screw 33. 'Insulator 2a may also be used to close lower opening Z6 of base cavity lil. Toggle spring 3h is then held with one of its indented edges in contact with knife edge t3@ of pivot member 32, and frame 3 with pivoted operating member liti@ mounted thereon is placed on the base by slightly parting legs 74B so that ears d3 of the base are received with slots '76 of the frame. Concurrently, knife edge i219 of the operating member is engaged with the other indented edge of toggle spring 3U. Bearing Il@ is then dropped in position on the edges lill@ of the operating member and the altitude adjusting assembly is added thereto. The cam follower sub-assembly, consisting of cam follower l39 with pivotally attached eyelet 137 is then pivotally mounted on connecting portion '7l of frame 3, so that lower annular surface i3d of pivoted eyelet i' rests on the upper shoulder of range spring 12d; The cover sub-assembly is then slipped into position with tongues 37 underneath tabs '74 of the frame. Downward pressure exerted at the rear end of cover plate 5a. seats the cover assembly in position on the frame with side flanges 89 thereof overlapping upper edges 92 of the frame, and with the edges of the cover plate 5a bridging bet-Ween lower edges 9S of tabs 'M and upper rear shoulders 92h of frame legs 70. Bellows assembly i may then be mounted on the frame. To mount the bellows assembly, spaced tabs i712 thereof are positioned Lunder tabs S5 of the frame. Clips 93 are then placed between indentations 91a of cover pla-te Sa and slots i174 of bellows cover ll'7tl, and the cover assembly S is thereby locked to bellows assembly i about connecting portion 7i of the frame. This completes the assembly operation of the cold control switch with only the differential and altitude screwV adjustments remaining to be made before the control is ready for service.

The simplicity of this improved switch permits the over-all dimensions to be small compared to other prior devices. elFor instance, in a cold control constructed in accordance with this invention, for controlling a two horsepower compressor, the device has an over-all length of 25/16 inches, a width of 1%2 inches, and a height of 17/16 inches, excluding the shaft.

While in accordance with the patent statutes, I have described what at present is considered to be the preferred embodiment of my invention, it will be obvious to those skilled in the art that .various changes and modifications may be made therein without departing from the invention, and I, therefore, aim in the following claims to cover all such equivalent variations as fall Within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A temperature responsive electric switch comprising an insulating base, a pair of contacts mounted on said base, a frame attached to said base, a contact operating member pivoted on said frame, said base having integrally formed fixed stops to limit the movement of said operating member, externa-l temperature responsive means carried by said frame for actuating said operating member for movement between said stops, a U-shaped toggle spring having an indented portion adjacent to each outer end, one of said outer ends of said spring serving as a relatively fixed pivot and the other of said outer ends being relatively movable, a linearly movable nonrotatable adjusting element, said toggle spring having its indented portions in continuous compression between said linearly movable nonrotatable adjusting element which bears upon the indented portion of the pivot end thereof and a movable end of said contact operating member which bears upon the indented portion of the relatively movable end thereof, said linearly movable adjusting element varying the compression upon said toggle spring at a knife edge point of contact with the indented portion of the pivot end of said spring, thereby to vary the temperature differential between the opposite movements of said operating member between said stops and guide means integrally formed with said base adjacent said stops for guiding the linear movement of said element, said base controlling the offset of the toggle spring.

2. The switch of claim 1 in which the pair of contacts mounted on the base includes one relatively fixed Contact, one relatively movable contact mating therewith, and a bounce damping means connected to the relatively movable contact, thereby to enhance the longevity of the contacts of said switch.

3. A temperature responsive electric switch comprising an insulating base, a pair of contacts mounted on said base, a frame attached to said base, a contact operating member pivoted on said frame, said base having fixed stops to limit the movement of said operating member, a U-shaped toggle spring in continuous compression between a movable edge of said operating member and an adjusting element, said toggle spring continuously biasing said operating member in the direction of one of said stops, a channel formed in said base, said adjusting element being slidably received in said channel and contacting said toggle spring in a knife edge engagement and being linearly movable to vary the force supplied by said toggle spring, external temperature responsive means carried by said frame for exerting a force upon said operating member to urge said operating member in the same direction as that toward which it is continuously biased by said toggle spring, and a coil spring urging said operating member in a direct-ion opposite that direction toward which the toggle spring biases said operating member, the biasing force exerted upon the movable edge of I said con-tact operating member by said toggle spring providing a snap acting force for movement or" said operating member toward said one of said stops when the su-m of the forces exerted upon said Contact operating member by said coil spring and said temperature responsive means is very small.

4. The switchk of claim 3 including a manual adjusting means for varying the compression of said coil spring, said manual adjusting means comprising a manually rotatable cam and a pivoted cam follower, said cam follower bearing against said coil spring to vary the compression thereof in response to the manual rotation of said cam.

`5. A condition responsive electric switch comprising an insulating base, a plurality of contacts with at least one of said contacts mounted on said base,'a contact operating member, supporting means pivotal-ly mounting said operating member, means including fixed stops to limit the movement of said operating member, external condition responsive means for actuating said opera-ting member for movement between said stops, toggle spring means continually biasing said operating member in a direction of one or' said stops, and a nonrotatable linearly movable adjusting element, and guide means formed in said base, said element guided by said guide means and engaged with said toggle spring with a knife edge contact for varying the biasing force supplied by said toggle spring means, thereby to vary the condi-tion differential between the opposite movements of said operating member between said stops.

References Cited by the Examiner UNITED STATES PATENTS 2,738,397 3/'56 Slonneger 200-8'3 `2,889,432 6/59 Miller 20G-83 2,930,865 3/60 Roeser 200-166 FOREIGN PATENTS 109, 107 i3 /28 Austria. 506,892 6/ 39 Great Britain. 738,497 \10/5\5 Great Bn'tain.

ROBERT K. SCHAEFER, Acting Primary Examiner. 

1. A TEMPERATURE RESPONSIVE ELECTRIC SWITCH COMPRISING AN INSULATING BASE, A PAIR OF CONTACTS MOUNTED ON SAID BASE, A FRAME ATTACHED TO SAID BADE, A CONTACT OPERATING MEMBER PIVOTED ON SAID FRAME, SAID BASE HAVING INTEGRALLY FORMED FIXED STOP TO LIMIT THE MOVEMENT OF SAID OPERATING MEMBER, EXTERNAL TEMPERATURE RESPONSIVE MEANS CARRIED BY SAID FRAME FOR ACTUATING SAID OPERATING MEMBER FOR MOVEMENT BETWEEN SAID STOPS, A U-SHAPED TOGGLE SPRING HAVING AN INDENTED PORTION ADJACENT TO EACH OUTER END, ONE OF SAID OUTER ENDS OF SAID SPRING SERVING AS A RELATIVELY FIXED PIVOT AND THE OTHER OF SAID OUTER ENDS BEING RELATIVELY MOVABLE, A LINEARLY MOVABLE NONROTATABLE ADJUSTING ELEMENT, SAID TOGGLE SPRING HAVING ITS INDENTED PORTIONS IN CONTINUOUS COMPRESSION BETWEEN SAID LINEARLY MOVABLE NONROTATABLE ADJUSTING ELEMENT WHICH BEARS UPON THE INDENTED PORTION OF THE PIVOT END THEREOF AND A MOVABLE END OF SAID CONTACT OPERATING MEMBER WHICH BEARS UPON THE INDENTED PORTION OF THE RELATIVELY MOVABLE END THEREOF, SAID LINEARLY MOVABLE ADJUSTING ELEMENT VARYING THE COMPRESSION UPON SAID TOGGLE SPRING AT A KNIFE EDGE POINT OF CONTACT WITH THE INDENTED PORTION OF THE PIVOT END OF SAID SPRING, THEREBY TO VARY THE TEMPERATURE DIFFERENTIAL BETWEEN THE OPPOSITE MOVEMENTS OF SAID OPERATING MEMBER BETWEEN SAID STOPS AND GUIDE MEANS INTEGRALLY FORMED WITH SAID BASE ADJACENT SAID STOPS FOR GUIDING THE LINEAR MOVEMENT OF SAID ELEMENT, SAID BASE CONTROLLING THE OFFSET OF THE TOGGLE SPRING. 